Ventricles of the brain contain cerebrospinal fluid which cushions the brain against shock and provides a means for nutrient and waste transport in the brain. Cerebrospinal fluid is constantly being secreted and absorbed by the body, usually in equilibrium. Cerebrospinal fluid is produced in the ventricles of the brain, where under normal conditions, it is circulated in the subarachnoid space and reabsorbed into the bloodstream, predominantly into the superior sagittal sinus via the arachnoid villi. However, if blockages exist in the circulation pathways of cerebrospinal fluid, perhaps in the ventricles, cerebrospinal fluid can't be reabsorbed by the body at the proper rate.
This imbalance can create a condition known as hydrocephalus: a condition marked by an excessive accumulation of fluid in subarachnoid space, including the cerebral ventricles. Hydrocephalus is a condition characterized by abnormal flow, absorption or formation of cerebrospinal fluid which may subsequently increase the volume and/or pressure of the intracranial cavity. If left untreated, the increased intracranial pressure can lead to neurological damage and may result in death.
Over the past 40 years, a common treatment for hydrocephalus patients has been the cerebrospinal fluid shunt. A standard shunt consists of the proximal (upstream) catheter, a valve and a distal (downstream or discharge) catheter. The excess cerebrospinal fluid is typically drained from the ventricles or other subarachnoid location to a suitable cavity, most often the peritoneum or the right atrium of the heart. A ventricular catheter is inserted into the brain through a burr hole in the skull. Alternatively, the proximal catheter can be placed between the vertebrae into the spinal subarachnoid space. The catheter placed into the subarachnoid space shunts cerebrospinal fluid to other areas of the body, where it can be reabsorbed. The presence of the shunt relieves pressure from cerebrospinal fluid on the brain.
A common complication for these implanted shunt systems is over-drainage, potentially resulting in slit ventricles, slit ventricle syndrome, loss of brain compliance, shunt occlusion, sub-dural hematoma or any of a number of other complications. Current methods for addressing this issue include the use of adjustable valves such as the STRATA™ and STRATA NSC™ valves (STRATA and STRATA NSC are trademarks of Medtronic, Inc., Minneapolis, Minn.). Over-drainage may still occur with the use of these valves due to significant intracranial pressure spikes.
Shunt valves are also prone to clogging. A clogged shunt valve could result in serious complications through failure to provide proper drainage of cerebrospinal fluid from the ventricles of the brain. Therefore it is desirable to avoid narrow passageways within the shunt system which could increase the incidence of shunt clogging and occlusion.